Re: [PATCH v4] nvdimm: btt_devs: fix a NULL pointer dereference

[Mukesh Ojha <mojha@codeaurora.org>]

On 3/26/2019 3:25 AM, Aditya Pakki wrote:
> In case kmemdup fails, the fix releases resources and returns to
> avoid the NULL pointer dereference.
>
> Signed-off-by: Aditya Pakki <pakki001@umn.edu>
>
> ---
> v3: Move kfree(nd_btt) to goto block.
> v2: Replace incorrect kfree with ida_simple_remove, suggested by
> Johannes Thumshirn
> v1: Free nd_btt->id in case of failure and avoid double free, suggested
> by Dan Williams
> ---
>   drivers/nvdimm/btt_devs.c | 18 +++++++++++++-----
>   1 file changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/nvdimm/btt_devs.c b/drivers/nvdimm/btt_devs.c
> index b72a303176c7..9486acc08402 100644
> --- a/drivers/nvdimm/btt_devs.c
> +++ b/drivers/nvdimm/btt_devs.c
> @@ -198,14 +198,15 @@ static struct device *__nd_btt_create(struct nd_region *nd_region,
>   		return NULL;
>   
>   	nd_btt->id = ida_simple_get(&nd_region->btt_ida, 0, 0, GFP_KERNEL);
> -	if (nd_btt->id < 0) {
> -		kfree(nd_btt);
> -		return NULL;
> -	}
> +	if (nd_btt->id < 0)
> +		goto out_nd_btt;
>   
>   	nd_btt->lbasize = lbasize;
> -	if (uuid)
> +	if (uuid) {
>   		uuid = kmemdup(uuid, 16, GFP_KERNEL);
> +		if (!uuid)
> +			goto out_put_id;
> +	}
>   	nd_btt->uuid = uuid;
>   	dev = &nd_btt->dev;
>   	dev_set_name(dev, "btt%d.%d", nd_region->id, nd_btt->id);
> @@ -220,6 +221,13 @@ static struct device *__nd_btt_create(struct nd_region *nd_region,
>   		return NULL;
>   	}
>   	return dev;
> +
> +out_put_id:
> +	ida_simple_remove(&nd_region->btt_ida, nd_btt->id);
> +
> +out_nd_btt:
> +	kfree(nd_btt);
> +	return NULL;
>   }
>   
>   struct device *nd_btt_create(struct nd_region *nd_region)


you have to take care of this below if block(true) as well as you are 
touching the function.
  if (ndns && !__nd_attach_ndns(&nd_btt->dev, ndns, &nd_btt->ndns)) {

Thanks,
Mukesh